Compositions For The Production Of Fracture-Tough Dental Parts By Means Of Stereolithography

ABSTRACT

A polymerizable composition, which includes (a) at least one radically polymerizable oligomer, (b) at least one radically polymerizable monomer and (c) at least one initiator for the radical polymerization, characterized in that the radically polymerizable oligomer (a) is selected from the group consisting of aliphatic urethane (meth)acrylate oligomers, epoxy (meth)acrylate oligomers and polyether urethane (meth)acrylate oligomers, and the radically polymerizable monomer (b) is polyfunctional.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims priority toU.S. patent application Ser. No. 16/705,892, filed on Dec. 6, 2019,which claims priority to European Patent Application No. 18215764.4filed on Dec. 21, 2018, all the disclosures of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to compositions which are suitable asdental material particularly for the production of dental parts, inparticular orthodontic appliances, using additive manufacturingprocesses, such as e.g. stereolithography.

BACKGROUND

Malpositions can be corrected not only with conventional orthodonticprocesses, e.g. by means of ceramic brackets, but also with the aid oforthodontic appliances. For example, the correction of malposition withtransparent plastic splints, so-called aligners, is already known fromthe 1940s. The transparent aligners completely cover the teeth and areto be worn for 22 hours a day and taken out only for teeth cleaning oreating and drinking. Elements for anchoring to the teeth, so-calledattachments, which make it possible for the aligners to be force-fittedonto the teeth, are often also constituents of the therapy. Theattachments allow controlled three-dimensional tooth movements to becarried out, such as are required for example for intrusion andextrusion or for derotation of rounded teeth such as canines orpremolars. A splint, a so-called positioner, is often also recommendedfor optimal fine adjustment of the teeth in the last phase of thetreatment with fixed braces. For the production of positioners andaligners, plaster models of both jaws are conventionally produced andeach individual tooth is separated from the model. Then the teeth in waxare re-placed into the optimal position, coated with silicone and curedin a special furnace.

As with other dental materials, certain demands are also to be made onthe mechanical properties of orthodontic appliances. For example, a highfracture toughness is advantageous, or even necessary, in the case oforthodontic splints, aligners, aligner attachments, positioners bearingaligner attachments, occlusal splints, transfer splints, drillingtemplates, prosthesis materials, prosthetic teeth, try-ins, i.e. aprosthesis with teeth printed out in one piece and one colour forinserting and checking the fit, and denture. When in use, such partshave to withstand deformations without breaking. In general, it is truefor all named materials that a high strength is advantageous at the sametime. Positioners bearing aligner attachments are e.g. clipped on overthe teeth, for which the positioners have to deform without breaking. Aspositioners and attachments have to be manufactured from the samematerial by reason of the process, this material must at the same timealso meet the demands made on the attachment, namely to have asufficiently high flexural modulus and a sufficiently high flexuralstrength.

To make use of computer-aided manufacturing processes it wouldfurthermore be desirable if such materials could be processed usingadditive processes. Such additive processes, which are also oftencombined under the term “Rapid Prototyping” (RP), have more recentlybeen used increasingly for the production of dental parts. By this ismeant manufacturing processes in which three-dimensional models orcomponents are produced in layers or continuously from computer-aideddesign data (CAD data) (A. Gebhardt, Vision of Rapid Prototyping, Ber.DGK 83 (2006) 7-12). These are processes, such as e.g. stereolithography(SL), selective laser sintering (SLS), 3D printing, fused depositionmodelling (FDM), inkjet printing (IJP), 3D plotting, multijet modelling(MJM), solid freeform fabrication (SFF), laminated object manufacturing(LOM), laser powder forming (LPF), with which models, components orshaped parts can be produced cost-effectively even on a small scale (A.Gebhardt, Generative Fertigungsverfahren, 3^(rd) Ed., Carl HanserVerlag, Munich 2007, 77 et seq.). In the case of stereolithography ashaped part is constructed in layers from a liquid and curable monomerresin on the basis of CAD data (A. Beil, Fertigung von Mikro-Bauteilenmittels Stereolithographie, Düsseldorf 2002, VDI-Verlag 3 et seq.).

These materials thus necessarily have to be light-curing and mustadditionally have a low viscosity, as otherwise they cannot be processedreadily in simple devices without heating and scraper.

Specifically for splints and aligner attachments, as little inherentcolour as possible with, at the same time, high transparency of thefinished parts is additionally particularly desirable.

SUMMARY

The object of the invention is thus to provide materials which meet theabove-named demands. In particular, the materials are to be light-curingand to have a low viscosity, with the result that they are to beprocessed in an additive manufacturing process, in particular with theaid of a stereolithographic printer. In addition, the cured materialsare to have a high fracture toughness, in particular a high outer fibrestrain, with at the same time a high flexural strength and a highflexural modulus and are to be characterized by a low level of inherentcolour and a high transparency.

DETAILED DESCRIPTION

According to the invention this object is achieved by polymerizablecompositions comprising (a) at least one radically polymerizableoligomer, (b) at least one radically polymerizable monomer and (c) atleast one initiator for the radical polymerization.

The compositions according to the invention are characterized in thatthe radically polymerizable oligomer (a) is selected from the groupconsisting of (i) aliphatic urethane (meth)acrylate oligomers, (ii)epoxy (meth)acrylate oligomers and (iii) polyether urethane(meth)acrylate oligomers, and the radically polymerizable monomer (b) ispolyfunctional.

The radically polymerizable oligomer (a) preferably has 1 to 6, inparticular 2 to 4, terminal (meth)acryl groups and is in particularselected from the group consisting of di- or tetrafunctional aliphaticurethane (meth)acrylate oligomers and difunctional epoxy (meth)acrylateoligomers. The urethane (meth)acrylate oligomers according to theinvention include in particular polyether urethane (meth)acrylateoligomers, as well as polyester urethane (meth)acrylate oligomers.

In a first particularly preferred embodiment the compositions accordingto the invention are characterized in that the radically polymerizableoligomer (a) is an oligomer (a1) which is obtainable by polymerizationof 2-hydroxyethyl (meth)acrylate,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane,ε-caprolactone and 2-(2-hydroxyethoxy)ethanol.

The oligomer (a1) preferably has a linear structure, wherein both chainends in each case are formed by 2-hydroxyethyl (meth)acrylate units,with the result that 2 free acrylate or methacrylate groups per oligomerare available for the radical polymerization with the polyfunctionalmonomer (b) and optionally further constituents. Furthermore, it ispreferred that the hydroxy groups of both terminal 2-hydroxyethyl(meth)acrylate radicals point towards the middle of the chain and eachform a urethane bond with one of the two cyano groups of1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane. Therespectively other cyano group of the1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane forms aurethane bond with hydroxy groups of a mid-chain segment, wherein themid-chain segment is obtainable by polymerization of ε-caprolactone and2-(2-hydroxyethoxy)ethanol or by polymerization of1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane,ε-caprolactone and 2-(2-hydroxyethoxy)ethanol.

In a preferred embodiment the oligomer (a1) can be described by thefollowing structural formula (I)

in which

R¹ and R⁵ each are —C(═O)—NH— or —C(═O)—NH—CH₂—,

R³ and R⁷ each are —NH—C(═O)—or CH₂—NH—C(═O)—,

R², R⁴, R⁶ and R⁸ each are H or CH₃,

R⁹ and R¹⁰ each are H or CH₃,

wherein,

if R¹ is —C(═O)—NH—, then R² is H, R³ is —CH₂—NH—C(═O)— and R⁴ is CH₃and,

if R¹ is —C(═O)—NH—CH₂—, then R² is CH₃, R³ is —NH—C(═O)— and R⁴ is H,

wherein R¹, R³, R⁵ and R⁷ each are inserted into the chain of structure(I) from left to right, and

M is a mid-chain segment which is obtainable by polymerization 30 ofε-caprolactone and 2-(2-hydroxyethoxy)ethanol or by polymerization of1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane,ε-caprolactone and 2-(2-hydroxyethoxy)ethanol.

The oligomer (a1) can preferably be described by the followingstructural formula (II)

in which

R¹ to R¹⁰ have the above meanings,

M′ is a mid-chain segment which is obtainable by polymerization ofε-caprolactone and 2-(2-hydroxyethoxy)ethanol, and n is a whole numberfrom 1 to 10, preferably 1 to 7, particularly preferably 1 to 5, such asfor instance 1 to 4 or 2 to 3, and in particular 1 or 2 and quiteparticularly preferably 1.

In an embodiment the mid-chain segment M′ in the above formula (II) isdescribed by structural formula (III)

wherein x is a number from 1 to 20, preferably 1 to 15, particularlypreferably 1 to 5, such as for instance 2 to 3, and y is a number from 1to 20, preferably 1 to 15, particularly preferably 1 to 5, such as forinstance 2 to 3.

It is particularly preferred that R⁹ and R¹⁰ each have the same meaning.In particular, R⁹ and R¹⁰ are both H, with the result that oligomer (a1)is selected from the group consisting of oligomers which are obtainableby polymerization of 2-hydroxyethyl acrylate,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane,ε-caprolactone and 2-(2-hydroxyethoxy)ethanol.

In a second particularly preferred embodiment the oligomer (a) is anoligomer (a2) which is obtainable by polymerization of 2-hydroxyethyl(meth) acrylate,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane, adipic acidand ethylene glycol.

In a preferred embodiment the oligomer (a2) can be described by theabove structural formula (I), in which R¹ to R¹⁰ have the above meaningand M is a mid-chain segment which is obtainable by polymerization ofadipic acid and ethylene glycol or by polymerization of1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane, adipic acidand ethylene glycol.

The oligomer (a2) can preferably be described by the above structuralformula (II), in which R¹ to R¹⁰ have the above meanings and M′ is amid-chain segment which is obtainable by polymerization of adipic acidand ethylene glycol, and n is a whole number from 1 to 10, preferably 1to 7, particularly preferably 1 to 5, such as for instance 1 to 4 or 2to 3, and in particular 1 or 2 and quite particularly preferably 1.

In an embodiment of oligomer (a2) the mid-chain segment M′ in the aboveformula (II) is described by structural formula (IV)

wherein x is a number from 1 to 20, preferably 1 to 15, particularlypreferably 1 to 5, such as for instance 2 to 4.

It is particularly preferred that R⁹ and R¹⁰ each have the same meaning.In particular, R⁹ and R¹⁰ are both H, with the result that oligomer (a2)is selected from the group consisting of oligomers which are obtainableby polymerization of 2-hydroxyethyl acrylate,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane, adipic acidand ethylene glycol.

In a third particularly preferred embodiment the oligomer (a) is anoligomer (a3) which is obtainable by polymerization of 2-hydroxyethyl(meth)acrylate, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane and tetrahydrofuran.

In a preferred embodiment the oligomer (a3) can be described by theabove structural formula (I), in which R¹ to R¹⁰ have the above meaningand M is a mid-chain segment which is obtainable by polymerization oftetrahydrofuran or by polymerization of1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane andtetrahydrofuran.

The oligomer (a3) can preferably be described by the above structuralformula (II), in which R¹ to R¹⁰ have the above meanings and M′ is amid-chain segment which is obtainable by polymerization oftetrahydrofuran, and n is a whole number from 1 to 10, preferably 1 to7, particularly preferably 1 to 5, such as for instance 1 to 4 or 2 to3, and in particular 1 or 2 and quite particularly preferably 1.

In an embodiment of oligomer (a3) the mid-chain segment M′ in the aboveformula (II) is described by structural formula (V)

wherein x is a number from 1 to 20, preferably 1 to 15, particularlypreferably 5 to 15, such as for instance 8 to 12.

It is particularly preferred that R⁹ and R¹⁰ each have the same meaning.In particular, R⁹ and R¹⁰ are both H, with the result that oligomer (a3)is selected from the group consisting of oligomers which are obtainableby polymerization of 2-hydroxyethyl acrylate,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane andtetrahydrofuran. Alternatively, R⁹ and R¹⁰ are both CH₃, with the resultthat oligomer (a3) is selected from the group consisting of oligomerswhich are obtainable by polymerization of 2-hydroxyethyl methacrylate,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane andtetrahydrofuran.

In a fourth particularly preferred embodiment the oligomer (a) is anoligomer (a4) which is obtainable by polymerization of 2-hydroxyethyl(meth)acrylate,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane and ethyleneglycol.

In a preferred embodiment the oligomer (a4) can be described by theabove structural formula (I), in which R¹ to R¹⁰ have the above meaningand M is a mid-chain segment which is obtainable by polymerization ofethylene glycol or by polymerization of1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane and ethyleneglycol.

The oligomer (a4) can preferably be described by the above structuralformula (II), in which R¹ to R¹⁰ have the above meanings and M′ is amid-chain segment which is obtainable by polymerization of ethyleneglycol, and n is a whole number from 1 to 10, preferably 1 to 7,particularly preferably 1 to 5, such as for instance 1 to 4 or 2 to 3,and in particular 1 or 2 and quite particularly preferably 1.

In an embodiment of oligomer (a4) the mid-chain segment M′ in the aboveformula (II) is described by structural formula (VI)

wherein x is a number from 1 to 20, preferably 1 to 15, particularlypreferably 5 to 15, such as for instance 6 to 11, such as e.g. 7 to 10.

It is particularly preferred that R⁹ and R¹⁰ each have the same meaning.In particular, R⁹ and R¹⁰ are both —CH₃, with the result that oligomer(a4) is selected from the group consisting of oligomers which areobtainable by polymerization of 2-hydroxyethyl methacrylate,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane and ethyleneglycol.

In a fifth particularly preferred embodiment the oligomer (a) is anoligomer (a5) which is obtainable by polymerization of 2-hydroxyethyl(meth)acrylate, 2,2,4-trimethylhexanediol diisocyanate and ethyleneglycol.

In a preferred embodiment the oligomer (a5) can be described by thefollowing structural formula (VII)

in which

R⁹ and R¹⁰ have the above meaning,

R¹¹to R²⁶ are H or CH₃,

wherein

-   -   either R¹¹, R¹² and R¹⁵ are CH₃ and R¹³, R¹⁴, R¹⁶, R¹⁷ and R¹⁸        are H    -   or R¹³, R¹⁷ and R¹⁸ are CH₃ and R¹¹, R¹², R¹⁴, R¹⁵ and R¹⁶ are        H, and    -   either R¹⁹, R²⁰ and R²³ are CH₃ and R²¹, R²², R²⁴, R²⁵ and R²⁶        are H    -   or R²¹, R²⁵ and R²⁶ are CH₃ and R¹⁹, R²⁰, R²², R²³ and R²⁴ are        H,

M′ is a mid-chain segment which is obtainable by polymerization ofethylene glycol, and

n is a whole number from 1 to 10, preferably 1 to 7, particularlypreferably 1 to 5, such as for instance 1 to 4 or 2 to 3, and inparticular 1 or 2.

In an embodiment of oligomer (a5) the mid-chain segment M′ in the aboveformula (VII) is described by structural formula

wherein x is a number from 1 to 20, preferably 1 to 15, particularlypreferably 5 to 15, such as for instance 6 to 11, such as e.g. 6 to .

It is particularly preferred that R⁹ and R¹⁰ each have the same meaning.In particular, R⁹ and R¹⁰ are both —CH₃, with the result that oligomer(a5) is selected from the group consisting of oligomers which areobtainable by polymerization of 2-hydroxyethyl methacrylate,2,2,4-trimethylhexanediol diisocyanate and ethylene glycol.

In a sixth particularly preferred embodiment the oligomer (a) is anoligomer (a6) which is obtainable by polymerization of 2-hydroxyethyl(meth)acrylate, 2,2,4-trimethylhexanediol diisocyanate andtetrahydrofuran.

In a preferred embodiment the oligomer (a6) can be described by theabove structural formula (VII), in which R⁹ to R²⁶ have the abovemeaning, M′ is a mid-chain segment which is obtainable by polymerizationof tetrahydrofuran, and n is a whole number from 1 to 10, preferably 1to 7, particularly preferably 1 to 5, such as for instance 1 to 4 or 2to 3, and in particular 1 or 2.

In an embodiment of oligomer (a6) the mid-chain segment M′ in the aboveformula (VII) is described by structural formula (IX)

wherein x is a number from 1 to 20, preferably 1 to 15, particularlypreferably 5 to 15, such as for instance 7 to 12, such as e.g. 8 to 11.

It is particularly preferred that R⁹ and R¹⁰ each have the same meaning.In particular, R⁹ and R¹⁰ are both —CH₃, with the result that oligomer(a6) is selected from the group consisting of oligomers which areobtainable by polymerization of 2-hydroxyethyl methacrylate,2,2,4-trimethylhexanediol diisocyanate and tetrahydrofuran.

In a seventh particularly preferred embodiment the oligomer (a) is anoligomer (a7) which is an aliphatic tetrafunctional urethanemethacrylate oligomer with a molar mass of from approximately 7000 to9000 g/mol, in particular approximately 8000 g/mol, measured by means ofGPC, and is preferably present in the form of a mixture with triethyleneglycol dimethacrylate, wherein the mixture preferably comprises 80 to 95wt.-%, in particular approximately 90 wt.-%, of oligomer (a7). Forexample, oligomer (a7) is Miramer U3400 NT, obtainable from MiwonSpecialty Chemical Co., Ltd.

In an eighth particularly preferred embodiment the oligomer (a) is anoligomer (a8) which is a difunctional epoxy acrylate oligomer with amolar mass of from approximately 6000 to 7000 g/mol, such as forinstance 6600 g/mol, such as e.g. Photocryl E207, obtainable from MiwonSpecialty Chemical Co., Ltd.

The composition according to the invention quite particularly preferablycontains the above-described oligomer (al) as oligomer (a).

The radically polymerizable oligomer (a) preferably has a molar mass(expressed as the number-average molecular weight Mn, which can becalculated, in particular in the case of polyester urethane oligomers,via the hydroxyl value of the polyester diol used in the synthesis aswell as the molar masses of the isocyanate and (meth)acrylate used forthe synthesis) of more than 500 g/mol, in particular 500 to 10,000g/mol, such as e.g. 500 to 8000 g/mol or 1000 to 7000 g/mol or 1000 to5000 g/mol, particularly preferably 500 to 3000 g/mol, such as e.g. 1200to 2500 g/mol. Furthermore, it is preferred that the radicallypolymerizable oligomer (a) has a viscosity of from 5 to 150, preferably10 to 50, in particular 20 to 25 Pas, measured by means of rotationalviscometry at 50° C.

The radically polymerizable oligomer (a) is present, relative to thetotal weight of the composition, preferably in an amount of from 25 to60 wt.-%, in particular 30 to 55 wt.-%, such as e.g. 32 to 50 wt.-%. Forthe case where the composition according to the invention contains afiller (f), as described below, the quantity of radically polymerizableoligomer (a) is preferably 38 to 42 wt.-%. For the case where thecomposition according to the invention does not contain a filler, thequantity of radically polymerizable oligomer (a) is preferably 40 to 55wt.-%, in particular 45 to 50 wt.-%.

It has surprisingly been found that the use of an above-describedoligomer (a) in combination with a polyfunctional monomer (b) and aninitiator (c) yields compositions which are light-curing andlow-viscosity, with the result that they can be processed usingstereolithographic processes, and the cured compositions have a highfracture toughness, in particular a high outer fibre strain, with at thesame time a high flexural strength and a high flexural modulus. Thecompositions according to the invention are thus outstandingly suitableas dental material, in particular for the production of orthodonticappliances such as aligners, aligner attachments and positioners.

The compositions according to the invention contain a polyfunctionalmonomer which is radically polymerizable as component (b). Bypolyfunctional monomers is meant compounds with two or more, preferably2 to 6, such as e.g. 2 to 3 or 2 to 4, radically polymerizable groups.The polyfunctional monomer (b) preferably has (meth)acrylates and/or(meth)acrylamides as radically polymerizable groups.

Particularly suitable polyfunctional monomers (b) are (meth)acrylic acidderivatives selected from the group consisting of bisphenol Adi(meth)acrylate, bis-G(M)A (an addition product of (meth)acrylic acidand bisphenol A diglycidyl ether), ethoxylated or propoxylated bisphenolA di(meth)acrylate, such as e.g. bisphenol A di(meth)acrylate with 3(SR-348c=methacrylate; SR-349=acrylate, from Sartomer) or 2(SR-348L=methacrylate, from Sartomer) ethoxy groups,2,2-bis[4-(2-(meth)acryloxypropoxy)phenyl]propane, UD(M)A (an additionproduct of 2-hydroxyethyl (meth)acrylate and 2,2,4- or2,4,4-trimethylhexamethylene-1,6-diisocyanate), di-, tri-, tetra-,penta-, hexa- or heptaethylene glycol di(meth)acrylate, di-, tri-,tetra-, penta-, hexa- or heptapropylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, ethoxylated or propoxylatedtrimethylolpropane tri(meth)acrylate, e.g. trimethylolpropanetriacrylate propoxylated 3 times (Sartomer SR-492) and tripropyleneglycol diacrylate, pentaerythritol tetra(meth)acrylate, as well asglycerol di- and tri(meth)acrylate, 1,4-butanediol di(meth)acrylate,1,10-decanediol di(meth)acrylate (D3MA), 1,12-dodecanedioldi(meth)acrylate, polyether (meth) acrylates, polyester (meth)acrylates,epoxy (meth)acrylates, urethane (meth) acrylates, tricyclodecanedimethanol di(meth)acrylate, N,N-dimethacrylamide, crosslinkingpyrrolidones such as 1,6-bis-(3-vinyl-2-pyrrolidonyl)hexane,bisacrylamides such as methylene or ethylene bisacrylamide andbis(meth)acrylamides such as N,N′-diethyl-1,3-bis(acrylamido)propane,1,3-bis(methacrylamido)propane, 1,4-bis(acrylamido)butane or1,4-bis(acryloyl)piperazine.

Di- and trifunctional acrylates and methacrylates with a molecularweight of <1000 g/mol, such as e.g. glycerol1,3-dimethacrylate-2-acetate, aliphatic urethane diacrylates, phthalicacid HEA ester (Photomer 4173), pyromellitic acid di-di-HEA ester(HEA=2-hydroxyethyl acrylate), bis-G(M)A (an addition product of(meth)acrylic acid and bisphenol A diglycidyl ether),2,2-bis[4-(2-(meth)acryloxypropoxy)phenyl]propane, UD(M)A, triethyleneglycol di(meth)acrylate (TEGD(M)A), 2-phenoxyethyl (meth)acrylate(acrylate SR339C from Sartomer/Arkema), tricyclodecane dimethanoldimethacrylate (CAS 43048-08-4) and FLKP crosslinker, i.e. the reactionproduct of 1,3-phenylenebis(propane-2,2-diylcarbamoyloxyethane-2,1-diyl)bis(2-methylacrylate) (CAS 178884-91-1), 2-{[(2-{-[2-methacryloyloxy)ethoxy] carbonyl}amino)propan-2-yl]phenyl}propan-2-yl)carbamoyl]oxy}propyl methacrylate (CAS1219495-43-8) and1,3-phenylenebis(propane-2,2-diylcarbamoyloxypropane-2,1-diyl)bis(2-methylacrylate) (CAS 138393-21-2), are particularly preferred.These monomers are characterized by a high reactivity, a high doublebond conversion, good mechanical properties, low polymerizationshrinkage and a relatively low viscosity. Compositions comprising UDMA,TEGDMA, bis-GMA, 2-phenoxyethyl acrylate (SR339C, from Sartomer/Arkema),glycerol 1,3-dimethacrylate-2-acetate or a mixture thereof, inparticular a mixture of UDMA, TEGDMA and 2-phenoxyethyl acrylate orpreferably a mixture of UDMA, TEGDMA and bis-GMA or a mixture of UDMAand TEGDMA or a mixture of UDMA, TEGDMA, bis-GMA and glycerol1,3-dimethacrylate-2-acetate, as component (b) are quite particularlypreferred.

The use of polyfunctional monomers (b) having polar groups, such as e.g.OH groups, amide groups, urethane groups and/or urea groups, has provedto be particularly advantageous. It is assumed that such polar groupscan lead to the formation of intermolecular hydrogen bridge bonds,whereby the fracture toughness of the cured composition is not reducedtoo strongly.

The radically polymerizable polyfunctional monomer (b) or a mixturethereof is present, relative to the total weight of the compositionaccording to the invention, preferably in an amount of from 30 to 65wt.-%, in particular 30 to 60 wt.-%, such as e.g. 35 to 50 wt.-%,particularly preferably 38 to 45 wt.-%, in particular 38 to 41 wt.-%.

In addition to the radically polymerizable oligomer (a) and theradically polymerizable, polyfunctional monomer (b), the compositionaccording to the invention can furthermore optionally contain one ormore monofunctional monomers (d). Particularly suitable monofunctionalmonomers (d) are monofunctional (meth)acrylates, such as e.g. methyl,ethyl, 2-hydroxyethyl, butyl, benzyl, tetrahydrofurfuryl or isobornyl(meth)acrylate, p-cumylphenoxyethylene glycol methacrylate (CMP-1E) anddicyclopentanyl methacrylate (CAS No. 34759-34-7). The compositionaccording to the invention particularly preferably containsdicyclopentanyl methacrylate and/or p-cumylphenoxyethylene glycolmethacrylate (CMP-1E) as monofunctional monomer (d).

The monofunctional monomer (d) is preferably present, relative to thetotal weight of the composition according to the invention, in an amountof from 0 to 15 wt.-%, particularly preferably 0 to 10 wt.-%, inparticular 5 to 10 wt.-% or 7 to 9 wt.-%.

Particular properties of the materials before and after curing can beinfluenced by a targeted combination of the monomers. In the case ofmixtures of monofunctional and difunctional monomers, for example, theviscosity and reactivity decrease as the monofunctional monomers contentdecreases. Mixtures of difunctional and trifunctional monomers have ahigher reactivity, wherein the reactivity increases as the trifunctionalmonomers content increases. However, the trifunctional monomers contentalso brings about a greater brittleness of the cured composition.Reactivity and viscosity of the uncured composition as well as thepolymerization shrinkage are moreover determined by the molar mass ofthe monomers, wherein as the molar mass increases the polymerizationshrinkage decreases, while the viscosity rises.

For combinations of oligomers (a) and monomers (b) or combinations ofoligomers (a), monomers (b) and monomers (d), on the other hand, nogeneral principles are known. Instead, it has surprisingly been found bythe inventors of the present invention that the use of the specificoligomer (a) in combination with polyfunctional monomers, in particularin combination with a mixture of UDMA, TEGDMA and bis-GMA as monomer(b), and optionally dicyclopentanyl methacrylate as monomer (d), leadsto materials with particularly favourable properties, namely tocompositions which can be processed with simple stereolithographicprocesses, which after curing have a high fracture toughness, inparticular a high outer fibre strain, with at the same time a highflexural strength and a high flexural modulus and which are additionallycharacterized by a low level of inherent colour and a high transparency.

Suitable photoinitiators (c) for initiating the radicalphotopolymerization are benzophenone, benzoin as well as derivativesthereof or a-diketones or derivatives thereof, such as9,10-phenanthrenequinone, 1-phenylpropane-1,2-dione, diacetyl or4,4′-dichlorobenzil. Preferably camphorquinone (CQ) and2,2-dimethoxy-2-phenylacetophenone and quite particularly preferablya-diketones in combination with amines, as reducing agent, are used,such as e.g. 4-(dimethylamino)benzoic acid ester (EDMAB),N,N-dimethylaminoethyl methacrylate, N,N-dimethyl-sym.-xylidine ortriethanolamine. Diethylthioxanthene (DETX, CAS 82799-44-8) andisopropylthioxanthone (ITX, CAS 75081-21-9), both in each casepreferably in combination with ethyl 4-(dimethylamino)benzoate (EMBO,CAS No. 10287-53-3), are further preferred. [1-/4-Phenylsulfanylbenzoyl)heptylideneamino] benzoate (Irgacure OXE 01) and[1[9-ethyl-6-(2-methylbenzoyl)carbazol-3-yl]ethylideneamino] acetate(Irgacure OXE 02) are also preferred.

Particularly preferred photoinitiators are furthermore Norrish type Iphotoinitiators, above all monoacyl- or bisacylphosphine oxides, such ase.g. diphenyl-(2,4,6-trimethylbenzoyl)phenylphosphine oxide (CAS No.75980-60-8), and in particular monoacyltrialkyl- or diacyldialkyl- ortetraacylgermanium compounds, such as e.g. benzoyltrimethylgermanium,dibenzoyldiethylgermanium, bis(4-methoxybenzoyl)diethylgermanium(MBDEGe), tetrakis(4-ethoxybenzoyl)germanium ortetrakis(4-propoxybenzoyl)germanium, or acyl tin compounds, such asmonoacyl stannanes, diacyl stannanes, triacyl stannanes or tetraacylstannanes, such as e.g. benzoyl triphenyltin. Further preferred acylgermanium compounds are described in EP 3 150 641 A1 and furtherpreferred acyl tin compounds are described in EP 3 293 215 Al. Mixturesof the different photoinitiators can also be used advantageously, suchas e.g. bis(4-methoxybenzoyl)diethylgermanium in combination withcamphorquinone and 4-dimethylaminobenzoic acid ethyl ester.

Camphorquinone (CAS No. 10373-78-1) in combination with ethyl4-(dimethylamino)benzoate (EMBO, CAS No. 10287-53-3) as well asphenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure 819, CAS162881-26-7), diphenyl(2,4,6-trimethylbenzoyl)phenylphosphine oxide(TPO, CAS No. 75980-60-8),2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone (Irgacure 369, CASNo. 119313-12-1),1-butanone-2-(dimethylamino)-2-(4-methylphenyl)methyl-1-4-(4-morpholinyl)phenyl(Irgacure 379, CAS No. 119344-86-4) and quite particularlybis(4-methoxybenzoyl)diethylgermanium (MBDEGe; Ivocerin),tetrakis(4-ethoxybenzoyl)germanium ortetrakis(4-propoxybenzoyl)germanium are quite particularly preferred. Inparticular, the preferred photoinitiators are those which either haveonly very little inherent colour or lose their colour when irradiatedwith light, e.g. in a stereolithographic printing process or in apost-tempering process.

The composition according to the invention contains the photoinitiator(c) preferably in an amount of from 0.1 to 3.0 wt.-%, in particular 0.5to 2 wt.-%, particularly preferably 0.7 to 1.5 wt.-%, such as e.g. 0.8to 1.3 wt.-%.

In addition to the above-mentioned components, the compositionsaccording to the invention can advantageously contain further additives.For the stereolithographic use, for example, compositions which containat least one UV absorber (e) are preferred.

The UV absorber serves to reduce the penetration depth of the light, andthus the polymerization depth, during the light-induced curing of thecomposition according to the invention. This proves to be advantageousin particular in the case of stereolithographic uses, as only thinlayers are to be cured in stereolithography. The use of a UV absorbercan thus improve the precision in stereolithographic processes. Inaddition, UV absorbers can also be added as colorant for aestheticpurposes.

As UV absorber or so-called colorant, organic dyes and pigments arepreferred, in particular azo dyes, carbonyl dyes, cyanine dyes,azomethines and methines, phthalocyanines and dioxazines. Dyes which aresoluble in the materials, in particular azo dyes, are particularlypreferred. Moreover, inorganic and in particular organic pigments whichcan be dispersed well in the materials are suitable as colorant. Azopigments and non-azo pigments are preferred. For example, UV absorbersbased on benzotriazole, benzophenone or triazines are particularlysuitable. Preferred UV absorbers are, for example,2,2′-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol](CAS No. 103597-45-1), 2,2′,4,4′-tetrahydroxybenzophenone (CAS No.131-55-5), 2-tert-butyl-6-(5-chloro-2H-benzotriazol-2-yl)-4-methylphenol(bumetrizole; CAS No. 3896-11-5),2,2′-benzene-1,4-diylbis(4h-3,1-benzoxazin-4-one) (CAS No. 18600-59-4),2-(4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-(octyloxy)phenol(CAS No. 2725-22-6), 2-(2-hydroxy-5-methylphenyl)benzotriazole (CAS No.2440-22-4), 2-(2-hydroxyphenyl)benzotriazole,2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (CAS No. 23328-53-2),2-(2′-hydroxy-3′,5′-di-t-butylphenyl)-5-chlorobenzotriazole (CAS No.3864-99-1), 2,2′-dihydroxy-4-methoxybenzophenone (CAS No. 131-53-3) and2,2′-dihydroxy-4,4′-dimethoxybenzophenone (CAS No. 131-54-4).

So-called Hindered Amine Light Stabilizers such asbis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (CAS No. 41556-26-7),methyl-1,2,2,6,6-pentamethyl-4-piperidyl sebacate (CAS No. 82919-37-7),bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate (CAS No.129757-67-1) and bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate (CASNo. 63843-89-0) are also suitable. Examples of further suitableso-called Hindered

Amine Light Stabilizers include compounds with CAS No. 52829-07-9, CASNo. 124172-53-8, CAS No. 65447-77-0, CAS No. 167078-06-0, CAS No.106990-43-6, CAS No. 70624-18-9, CAS No. 82451-48-7, CAS No. 136504-96-6or CAS No. 191743-75-6.

The composition according to the invention particularly preferablycontains bumetrizole as UV absorber. In an alternative preferredembodiment the UV absorber is 2,2′,4,4′-tetrahydroxybenzophenone.

The composition preferably contains at least one UV absorber, which hasan absorption maximum which corresponds to the wavelength of the lightused for the curing. UV absorbers with an absorption maximum below 400nm or in the range of from 350 to 550 nm, preferably 380 to 480 nm, arevery advantageous.

In a preferred embodiment, the composition according to the inventionfurthermore contains an optical brightener (h) in addition to a UVabsorber (e). The optical brightener (h) preferably absorbs light in theUV range, i.e. below 400 nm. It is thereby possible to reduce thepenetration depth of the light, and thus the polymerization depth, andincrease the precision in the case of stereolithographic uses. Moreover,the optical brightener is preferably capable of emitting light absorbedin the UV range as light with a wavelength of from 400 to 450 nm. Thus,the optical brightener can furthermore lead to an increase in thereactivity of the composition, as the brightener re-emits the absorbedlight as blue light because of its fluorescence, and thus providesadditional light power for photoinitiation.

The optical brightener (h) is preferably selected from the groupconsisting of 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (CAS No.7128-64-5) and fluorescent agents in the form of terephthalic acidderivatives, such as e.g. terephthalic acid derivatives which areobtainable e.g. under the name Lumilux blue LZ from Honeywell SpecialtyChemicals Seelze, Germany, or diethyl 2,5-dihydroxyterephthalate (CASNo. 5870-38-2).

The UV absorber (e) is preferably present, relative to the total weightof the composition according to the invention, in an amount of from 0 to2.0 wt.-%, particularly preferably 0.0001 to 0.5 wt.-%. In the case ofbumetrizole as UV absorber, the amount thereof is preferably 0.01 to 0.2wt.-%, particularly preferably 0.02 to 0.15 wt.-%. In the case of2,2′,4,4′-tetrahydroxybenzophenone as UV absorber, the amount ispreferably smaller, and in particular is 0.01 to 0.07 wt.-%. Thequantity of UV absorber (e) is smaller in the case of compositions whichcontain one or more fillers than in the case of unfilled compositions.

Furthermore, it is preferred that the optical brightener (h) is present,relative to the total weight of the composition according to theinvention, in an amount of from 0.001 to 0.1 wt.-%, preferably 0.002 to0.05 wt.-%, particularly preferably 0.005 to 0.02 wt.-%.

Moreover, it is preferred that the ratio by weight of UV absorber (e) tooptical brightener (h) is from 2:1 to 50:1, preferably from 2:1 to 30:1,particularly preferably from 2:1 to 5:1 or from 10:1 to 25:1.

It has been found that such combinations of UV absorber (e) and opticalbrightener (h) after curing of the composition according to theinvention lead to particularly transparent materials without visuallyperceptible inherent colour.

Particularly ideal results with particularly high transparency andparticularly little inherent colour can be achieved if the compositionaccording to the invention contains 2,2′,4,4′-tetrahydroxybenzophenoneor bumetrizole as UV absorber (e) and2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene as optical brightener(h). In particular, the composition according to the invention contains2,2′,4,4′-tetrahydroxybenzophenone and2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene in a ratio by weight offrom 2:1 to 10:1, preferably from 2:1 to 5:1, or bumetrizole and2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene in a ratio by weight offrom 5:1 to 30:1, preferably from 10:1 to 20:1.

The compositions according to the invention can moreover containparticulate filler (f). In general, inorganic and/or organic particlescan be used as fillers. The filler or fillers preferably has/have aparticle size of less than 25 μm, preferably less than 10 μm andparticularly preferably less than 5 μm. All particle sizes herein are,unless otherwise indicated, D50 values, i.e. 50 vol.-% of the particleshave a diameter which is smaller than the value indicated. Fillers serveprimarily to adjust the viscosity of the curable composition as well asthe mechanical and/or optical properties of the cured materials.Furthermore, it is preferred that the maximum particle size is smallerthan the thickness of the layers generated by stereolithography.Particles with a maximum size of 25 μm, preferably at most 15 μm, arepreferred.

The surface of the fillers can be modified, for example in order toimprove the dispersibility of the fillers in the organic matrix of thecomposition according to the invention. Those compounds which arechemically bonded, i.e. by ionic or covalent bonds, to the surface ofthe fillers are preferably used for the surface modification. Compoundswhich contain either acid groups, preferably carboxylic acid groups,phosphonic acid groups, hydrogen phosphate groups or acidic phosphoricacid ester groups, or silyl groups, preferably alkoxysilyl groups, arepreferred. The particle surface can be partially or preferablycompletely covered with the modifier. The modifiers used according tothe invention are monomeric compounds. Linear carboxylic acids, such ase.g. formic acid, acetic acid, propionic acid, octanoic acid, isobutyricacid, isovaleric acid, pivalic acid, or phosphonic acids, e.g. such asmethyl-, ethyl-, propyl-, butyl-, hexyl-, octyl- or phenylphosphonicacid, are particularly suitable as surface modifier. Silanes such aspropyltrimethoxysilane, phenyltrimethoxysilane, hexyltrimethoxysilane,octyltrimethoxysilane, trimethylchlorosilane, trimethylbromosilane,trimethylmethoxysilane and hexamethyldisilazane are preferred ascompounds containing silyl groups. Quite particularly preferred surfacemodifiers are acidic phosphoric acid esters, such as e.g. dimethyl,diethyl, dipropyl, dibutyl, dipentyl, dihexyl, dioctyl ordi(2-ethylhexyl) phosphate. The surface modifiers can also haveradically polymerizable groups, for example (meth)acrylate groups, whichreact with the component (a) and are thus incorporated into the polymernetwork.

Preferred fillers are particulate waxes, in particular carnauba wax,preferably with a particle size of from 1 to 10 μm, crosslinkedpolymethyl methacrylate (PMMA) particles, preferably with a particlesize of from 500 nm to 10 μm, as well as polyamide 12 particles,preferably with a particle size of from 5 to 10 μm. Quite particularlypreferred fillers are glass fillers, in particular glass fillers whichbefore any surface modification have a particle size of from 0.2 to 2.0μm, preferably 0.5 to 1.5 μm. Likewise particularly preferably, thecomposition contains a so-called prepolymer filler or isofiller, i.e. aground composite material which preferably has a broad particle-sizedistribution, e.g. with particle sizes of from 0.05 to 20 μm, inparticular approximately 0.1 to approximately 10 μm. In an embodiment,the prepolymer filler or isofiller preferably has a bimodalparticle-size distribution, wherein preferably more than 50%, inparticular more than 70% and particularly preferably more than 80% ofthe filler particles have a particle size of from 1 to 15 μm, measuredby means of laser diffraction with a CILAS 1064 particle-size measuringdevice in water with Teepol dispersant (Teepol L from BDH LaboratorySUPPLIES; Poole BH15 1TD, England) accompanied by ultrasonic dispersion.The prepolymer filler or isofiller is preferably surface-modified, inparticular silanized. In the case of surface-modified prepolymer fillersor isofillers, the above-mentioned particle sizes relate to the particlesizes before the surface modification, i.e. of the fillers before e.g.silanization.

In a preferred embodiment, the composition according to the inventioncontains a mixture of two or more fillers, in particular of two or morefillers with different particle sizes. It has been found that the use ofsuch filler mixtures does not increase the viscosity of the compositionexcessively and the compositions can therefore furthermore be processedwith additive processes, such as e.g. using stereolithography. A mixtureof a silanized glass filler (i) with a particle size of approximately0.7 μm (before the silanization), a silanized glass filler (ii) with aparticle size of approximately 1.0 μm (before the silanization) and aprepolymer filler (iii) with a broad particle-size distribution of fromapproximately 0.1 to approximately 10 μm is particularly preferred.Furthermore, it is quite particularly preferred that the compositionaccording to the invention contains, relative to its total weight, 2.0to 4.0 wt.-%, in particular 2.5 to 3.5 wt.-%, of glass filler (i), 0.5to 2.0 wt.-%, in particular 1.0 to 1.6 wt.-%, of glass filler (ii) and4.0 to 6.0 wt.-%, in particular 4.5 to 5.5 wt.-%, of prepolymer filler(iii).

In an alternative preferred embodiment, the composition according to theinvention is free of fillers (f).

In general, the composition according to the invention preferablycontains 0 to 15 vol.-% of filler(s) (f). This preferably corresponds toan amount of from 0 to 40 wt.-%, in particular 0 to 20 wt.-% andparticularly preferably 0 wt.-% or 6.0 to 20.0 wt.-%, such as e.g. 8.0to 15.0 wt.-% or 8.0 to 10.0 wt.-%, of filler (f), relative to the totalweight of the composition according to the invention.

In cases where the composition according to the invention comprises oneor more fillers (f), the composition preferably furthermore alsocontains a thixotropic additive (g). This additive (g) represents athickening agent and serves to prevent a sedimentation of the fillers inthe composition. In order not to increase the viscosity of thecomposition too strongly, the composition preferably contains only smallamounts of thixotropic additive (g), such as e.g. 0 to 3.0 wt.-%, inparticular 0 to 2.0 wt.-%, particularly preferably 0.1 to 2.0 wt.-% or0.5 to 2.0 wt.-%, relative to the total weight of the composition.Preferred thixotropic additives (g) are in particular selected from thegroup consisting of SiO₂, highly disperse SiO₂, i.e. SiO₂ with a smallprimary particle size and a large surface area, polymers, blockcopolymers and sheet silicates.

In addition to the above-mentioned components, the compositionsaccording to the invention can contain one or more further additives.

For example, the compositions can contain one or more polymerizationinhibitors. The polymerization inhibitor or inhibitors serves/serve asstabilizer to prevent a spontaneous polyreaction. The inhibitors orstabilizers improve the storage stability of the compositions and inaddition prevent an uncontrolled polyreaction in the stereolithographytank. The inhibitors are preferably added in such an amount that thecompositions are storage-stable over a period of approx. 2-3 years. Theinhibitors are particularly preferably used in an amount of from 0.001to 1.0 wt.-%, quite particularly preferably 0.001 to 0.20 wt.-%, in eachcase relative to the total mass of the composition.

It is preferred to use so-called aerobic inhibitors like phenols, suchas hydroquinone monomethyl ether (MEHQ) or2,6-di-tert.-butyl-4-methylphenol (BHT), which are effectively activeonly in the presence of oxygen and are preferably used in aconcentration range of 100-2000 ppmw. Suitable anaerobic inhibitors arephenothiazine, 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO),iodine and copper(I) iodide. These are already active in lowconcentrations of preferably 10-200 ppmw even in the absence of oxygen.Polymerization does not take place until these additives are consumed.It is advantageous here to use a mixture of aerobic and anaerobicinhibitors.

Aerobic inhibitors are preferably used in an amount of from 0.001 to0.50 wt.-% and anaerobic inhibitors in an amount of from 0.001 to 0.02wt.-%, in each case relative to the total mass of the composition.Preferred mixtures contain 0.005-0.10 wt.-% of aerobic inhibitors and0.001-0.02 wt.-% of anaerobic inhibitors, likewise relative to the totalmass of the composition.

The compositions according to the invention therefore preferably havethe following composition:

-   -   (a) 25 to 60 wt.-%, in particular 30 to 55 wt.-%, such as e.g.        32 to 50 wt.-%, particularly preferably 38 to 42 wt.-%,        oligomer, preferably oligomer (a1),    -   (b) 30 to 65 wt.-%, in particular 30 to 60 wt.-%, more        preferably 35 to 50 wt.-%, particularly preferably 38 to 45        wt.-%, in particular 38 to 41 wt.-%, polyfunctional monomer,    -   (c) 0.1 to 3.0 wt.-%, in particular 0.5 to 2 wt.-%, particularly        preferably 0.7 to 1.5 wt.-%, in particular 0.8 to 1.3 wt.-%,        photoinitiator,    -   (d) 0 to 15 wt.-%, particularly preferably 0 to 10 wt.-%, in        particular 5 to 10 wt.-% or 7 to 9 wt.-%, monofunctional        monomer,    -   (e) 0 to 2.0 wt.-%, particularly preferably 0.0001 to 0.5 wt.-%,        UV absorber,    -   (f) 0 to 40 wt.-%, in particular 0 to 20 wt.-%, particularly        preferably 0 wt.-% or 6.0 to 20.0 wt.-%, in particular 8.0 to        15.0 wt.-% or 8.0 to 10.0 wt.-%, filler and    -   (g) 0 to 3.0 wt.-%, in particular 0 to 2.0 wt.-%, particularly        preferably 0.1 to 2.0 wt.-% or 0.5 to 2.0 wt.-%, thixotropic        additive,

in each case relative to the total weight of the composition.

A quite particularly preferred composition comprises:

-   -   (a) 40 to 60 wt.-%, in particular 45 to 55 wt.-%, such as e.g.        48 to 52 wt.-%, oligomer, preferably oligomer (al),    -   (b) 40 to 60 wt.-%, in particular 45 to 55 wt.-%, particularly        preferably 46 to 52 wt.-%, polyfunctional monomer, wherein the        polyfunctional monomer is preferably a mixture of UDMA, TEGDMA        and bis-GMA,    -   (c) 0.5 to 2 wt.-%, particularly preferably 0.7 to 1.5 wt.-%, in        particular 0.8 to 1.3 wt.-%, photoinitiator,    -   (d) 0 to 10 wt.-%, particularly preferably 0 to 5 wt.-%, in        particular 0 wt.-%, monofunctional monomer,    -   (e) 0 to 2.0 wt.-%, particularly preferably 0.01 to 0.5 wt.-%,        particularly preferably 0.05 to 0.3 wt.-%, UV absorber,    -   (f) 0 to 40 wt.-%, in particular 0 to 20 wt.-%, particularly        preferably 0 wt.-%, filler and    -   (g) 0 to 3.0 wt.-%, in particular 0 to 2.0 wt.-%, particularly        preferably 0 wt.-%, thixotropic additive,

in each case relative to the total weight of the composition,

wherein the mixture of UDMA, TEGDMA and bis-GMA preferably comprises,relative to the total weight of the composition,

-   -   (b1) 10 to 20 wt.-%, particularly preferably 12 to 18 wt.-%,        UDMA,    -   (b2) 20 to 35 wt.-%, particularly preferably 25 to 33 wt.-%,        TEGDMA and    -   (b3) 3 to 20 wt.-%, particularly preferably 3 to 10 wt.-%,        bis-GMA.

In a further quite preferred embodiment the composition comprises:

-   -   (a) 37 to 55 wt.-%, in particular 39 to 47 wt.-%, such as e.g.        43 to 46 wt.-%, oligomer, preferably oligomer (al),    -   (b) 39 to 56 wt.-%, in particular 42 to 47 wt.-%, polyfunctional        monomer, wherein the polyfunctional monomer is preferably a        mixture of UDMA, TEGDMA and bis-GMA,    -   (c) 0.5 to 2 wt.-%, particularly preferably 0.7 to 1.5 wt.-%, in        particular 0.8 to 1.3 wt.-%, photoinitiator,    -   (d) 0 to 15 wt.-%, particularly preferably 7 to 14 wt.-%, in        particular 8 to 12 wt.-%, monofunctional monomer, wherein the        monofunctional monomer (a) preferably comprises dicyclopentanyl        methacrylate and/or p-cumylphenoxyethylene glycol methacrylate        and in particular dicyclopentanyl methacrylate,    -   (e) 0 to 2.0 wt.-%, particularly preferably 0.001 to 0.5 wt.-%,        particularly preferably 0.01 to 0.1 wt.-%, UV absorber,    -   (f) 0 to 40 wt.-%, in particular 0 to 20 wt.-%, particularly        preferably 0 wt.-%, filler and    -   (g) 0 to 3.0 wt.-%, in particular 0 to 2.0 wt.-%, particularly        preferably 0 wt.-%, thixotropic additive,

in each case relative to the total weight of the composition,

wherein the mixture of UDMA, TEGDMA and bis-GMA preferably comprises,relative to the total weight of the composition,

-   -   (b1) 10 to 20 wt.-%, particularly preferably 12 to 16 wt.-%,        UDMA,    -   (b2) 20 to 35 wt.-%, particularly preferably 21 to 29 wt.-%,        TEGDMA and    -   (b3) 3 to 20 wt.-%, particularly preferably 3 to 10 wt.-%,        bis-GMA.

In a further quite preferred embodiment the composition comprises:

-   -   (a) 37 to 55 wt.-%, in particular 38 to 44 wt.-%, such as e.g.        39 to 42 wt.-%, oligomer, preferably oligomer (a1),    -   (b) 35 to 50 wt.-%, in particular 37 to 42 wt.-%, polyfunctional        monomer, wherein the polyfunctional monomer is preferably a        mixture of UDMA, TEGDMA and bis-GMA,    -   (c) 0.5 to 2 wt.-%, particularly preferably 0.7 to 1.5 wt.-%, in        particular 0.8 to 1.3 wt.-%, photoinitiator,    -   (d) 0 to 15 wt.-%, particularly preferably 7 to 14 wt.-%, in        particular 8 to 12 wt.-%, monofunctional monomer, wherein the        monofunctional monomer (a) preferably comprises dicyclopentanyl        methacrylate and/or p-cumylphenoxyethylene glycol methacrylate        and in particular dicyclopentanyl methacrylate,    -   (e) 0 to 2.0 wt.-%, particularly preferably 0.001 to 0.5 wt.-%,        particularly preferably 0.01 to 0.1 wt.-%, UV absorber,    -   (f) 0 to 40 wt.-%, in particular 0 to 20 wt.-%, particularly        preferably 7 to 15 wt.-% or 8 to 12 wt.-%, filler, wherein the        filler is preferably a mixture of the above-described fillers        (i), (ii) and (iii), and    -   (g) 0 to 3.0 wt.-%, in particular 0.1 to 2.0 wt.-%, particularly        preferably 0.5 to 1.6 wt.-%, thixotropic additive, wherein the        thixotropic additive is preferably SiO₂,

in each case relative to the total weight of the composition,

wherein the mixture of UDMA, TEGDMA and bis-GMA preferably comprises,relative to the total weight of the composition,

-   -   (b1) 10 to 20 wt.-%, particularly preferably 10 to 15 wt.-%,        UDMA,    -   (b2) 20 to 35 wt.-%, particularly preferably 21 to 26 wt.-%,        TEGDMA and    -   (b3) 3 to 20 wt.-%, particularly preferably 3 to 8 wt.-%,        bis-GMA.

The rheological properties of the compositions according to theinvention are matched to the desired intended use. Materials forstereolithographic processing are preferably adjusted such that theirviscosity lies in the range of from 50 mPa·s to 100 Pa·s, preferably 100mPa·s to 10 Pa·s, particularly preferably 100 mPa·s to 5 Pa·s. Theviscosity is determined with a cone-plate viscometer at the desiredprocessing temperature for the materials (shear rate 100/s). Theprocessing temperature preferably lies in the range of from 10 to 70°C., particularly preferably 20 to 30° C. The composition according tothe invention particularly preferably has a viscosity <10 Pa·s at 25° C.Because of the low viscosity, the composition according to the inventionis suitable for being cured using additive manufacturing processes, suchas e.g. 3D printing or stereolithography.

In addition, the composition according to the invention is characterizedin that before and in particular even after the light curing it has ahigh transparency and little inherent colour.

In addition, the composition according to the invention is characterizedin that the materials obtained after the curing have a high fracturetoughness. Dentals parts which are obtained by curing the compositionaccording to the invention thus, to a high degree, withstanddeformations without breaking. A cured part preferably has an outerfibre strain of more than 7%, in particular an outer fibre strain ofmore than 10%, particularly preferably an outer fibre strain of morethan 11%, such as e.g. an outer fibre strain of 12%. The outer-fibrestrain is determined in a three-point flexural test according to ISO4049 with a support span of 20 mm, wherein a length sensor is arrangedon the underside of the test piece in order to determine the exactbending on the underside of the sample piece. The outer fibre strain inpercent (ε_(f)) is calculated using the formula ε_(f)=(600·s1·h)/L²,wherein s1 is the bending at break of the test piece, measured on theunderside of the test piece, h is the height of the test piece and L isthe support span. After the curing the composition according to theinvention particularly preferably has such an outer fibre strain thattest pieces do not break during a flexural test according to ISO 4049with a support span of 20 mm at a bending of 4 mm.

Moreover, the composition according to the invention is characterized inthat the materials obtained after the curing have a high flexuralstrength and a high flexural modulus. Parts which are obtained by curingthe composition according to the invention thus have a high stiffnessand oppose a deformation with a high level of resistance. A cured partpreferably has a flexural strength, determined according to ISO 4049, offrom 40 to 140 MPa, in particular a flexural strength of 50 MPa or more,such as e.g. 50 to 80 MPa, particularly preferably a flexural strengthof more than 55 MPa. Furthermore, a cured part preferably has a flexuralmodulus, determined according to ISO 4049, of from 800 to 3800 MPa, suchas 1000 to 2500 MPa, in particular a flexural modulus of more than 1000MPa, particularly preferably a flexural modulus of more than 1200 MPa ormore than 1300 or more than 1500 or more than 1800 MPa.

In addition, the composition according to the invention is characterizedin that the materials obtained after the curing have a high fracturetoughness and a high fracture work. A dental part which is obtainable bycuring the composition according to the invention preferably has afracture toughness K_(max) of from 0.5 to 1.8 MPa·m^(1/2), in particularof at least 0.6 MPa·m^(1/2), particularly preferably at least 0.8MPa·m^(1/2) or at least 1.0 MPa·m^(1/2) or at least 1.2 MPa·m^(1/2),and/or a fracture work FW of from 70 to 600 J/m², such as e.g. 100 to450 J/m², in particular of at least 110 J/m², particularly preferably atleast 150 J/m² or at least 180 J/m² or at least 250 J/m², wherein thefracture toughness K_(max) and the fracture work FW are determinedaccording to the test method described below.

Because of the above properties, compositions according to the inventionare outstandingly suitable as dental material and in particular for theproduction or repair of dental parts. The present invention thereforealso relates to the use of a composition according to the invention asdental material and in particular for the production or repair of dentalparts, such as e.g. dental restorations, prostheses, prosthesismaterials, artificial teeth, inlays, onlays, crowns, bridges, drillingtemplates, try-ins or orthodontic appliances. The composition accordingto the invention is particularly preferably suitable for the productionof orthodontic appliances, in particular aligners, positioners, alignerattachments, positioners bearing aligner attachments, occlusal splints,transfer splints or orthodontic splints.

The present invention therefore also relates to a process for theproduction of dental parts, in particular for the production of theabove-named dental parts, in which a composition according to theinvention is cured with the aid of light in order to yield the dentalpart. Furthermore, the invention also relates to dental parts, inparticular the above-mentioned parts, which are obtainable through sucha process.

The production or repair of dental parts is effected in particularextraorally. In addition, it is preferred that the production or repairof dental parts is effected through an additive process, in particularusing 3D printing or a lithography-based process, such as e.g.stereolithography.

The production of the dental part according to the invention ispreferably effected through a stereolithographic process. For thispurpose, a virtual copy of the tooth situation is created by direct orindirect digitization of the tooth to be restored or of the teeth to berestored on a computer, then a model of the dental restoration isconstructed on the computer on the basis of this copy and this model isthen produced by additive stereolithographic manufacturing. Theproduction of an orthodontic appliance using a stereolithographicprocess is carried out correspondingly. Once a virtual model of theorthodontic appliance to be produced has been created, the compositionaccording to the invention is polymerized by selective lightirradiation. The geometry of the orthodontic appliance can beconstructed in layers by polymerizing a plurality of thin layers withthe desired cross section one after another. The layered construction ofthe geometry is usually followed by a cleaning of the dental part bytreatment with a suitable solvent, such as e.g. an alcohol, such asethanol or isopropanol, a ketone, a ketal or an ester, and apost-treatment by irradiation of the dental part with a suitablewavelength, such as e.g. an irradiation with an intensity of 25 mW/cm²at 405 nm and at the same time 130 mW at 406 nm for 15 min, in which thedental part is irradiated with light of a suitable wavelength in orderto further reduce the residual monomer content and improve themechanical properties.

The invention is explained in more detail in the following withreference to embodiment examples.

EMBODIMENT EXAMPLES Examples 1 to 14

The components listed in Tables 1 to 2 were mixed homogeneously witheach other in the quantities indicated. For this purpose, except for theglass fillers and prepolymer fillers, all solid components weredissolved in the monomers, accompanied by stirring, for approximately 60min in a stirring unit with dissolver disc. The oligomer was then addedand it was stirred until a homogeneous mixture was achieved(approximately 60 min). Unfilled compositions (see Examples 1 to 7 and11) were then ready for use. For the case where the composition containsa filler (see Examples 8 to 10 and 12 to 14), this was then stirred inwith the aid of the stirring unit within 15 min, then milled twice bymeans of a rotary milling machine and then stirred again for 15 min.

10

TABLE 1 Compositions for the production of e.g. splints or drillingtemplates Composition [wt.-%] Component 1 2 3 4 5 6 TEGDMA¹⁾ 23.0 23.023.0 23.0 23.0 29.0 UDMA²⁾ 18.0 18.0 18.0 18.0 18.0 15.0 bis-GMA³⁾ 18.018.0 18.0 18.0 18.0 5.0 Oligomer (a1)⁴⁾ — — — — 40.0 50.0 Oligomer(a3)⁵⁾ 40.0 — — — — — Oligomer (a5)⁶⁾ — 40.0 — — — — Oligomer (a4)⁷⁾ — —40.0 — — — Oligomer (a3)⁸⁾ — — — 40.0 — — TPO⁹⁾ 0.85 0.85 0.85 0.85 0.850.85 Bumetrizole 0.15 0.15 0.15 0.15 0.15 0.15 Viscosity (23° C.) 4.81.3 5.2 — 5.6 3.2 oscill. [MPa*s] Kmax [MPa m^(1/2)] 0.8 0.8 0.8 0.9 1.2— wet FW [J/m²] wet 147 114 99 169 189 — ¹⁾Triethylene glycoldimethacrylate (CAS No. 109-16-0) ²⁾Urethane dimethacrylate (CAS No.72869-86-4) ³⁾Addition product of methacrylic acid and bisphenol Adiglycidyl ether ⁴⁾Oligomer (a1) with R⁹ and R¹⁰ = H and a molar mass ofapprox. 2200 g/mol ⁵⁾Oligomer (a3) with R⁹ and R¹⁰ = CH₃ ⁶⁾Oligomer (a5)with R⁹ and R¹⁰ = CH₃ ⁷⁾Oligomer (a4) with R⁹ and R¹⁰ = CH₃ ⁵⁾Oligomer(a3) with R⁹ and R¹⁰ = H⁹⁾Diphenyl(2,4,6-trimethylbenzoyl)phenylphosphine oxide (CAS No.75980-60-8)

TABLE 2 Compositions for the production of e.g. positioners bearingaligner attachments Composition [wt.-%] Component 7 8 9 10 11 12 13 14TEGDMA¹⁾ 25.70 23.26 20.82 18.39 25.70 23.26 20.82 18.39 UDMA²⁾ 13.2712.01 10.75 9.49 13.27 12.01 10.75 9.49 bis-GMA³⁾ 5.00 4.53 4.05 3.585.00 4.53 4.05 3.58 Glycerol 1,3-dimethacrylate- 10.00 9.05 8.10 7.15 —— — — 2-acetate⁴⁾ Dicyclopentanyl methacrylate⁵⁾ — — — — 10.00 9.05 8.107.15 Oligomer (a1)⁶⁾ 45.00 40.73 36.46 32.20 45.00 40.73 36.46 32.20TPO⁷⁾ 1.00 0.91 0.81 0.72 1.00 0.91 0.81 0.72 Bumetrizole 0.03 0.02 0.020.02 0.03 0.02 0.02 0.02 Glass filler⁸⁾ — 4.45 8.90 13.34 — 4.45 8.9013.34 Prepolymer filler⁹⁾ — 5.04 10.09 15.11 — 5.04 10.09 15.11Viscosity (23° C.) oscill. ~2.0 2.0 2.9 5.0 2.0 2.1 3.1 7.0 [MPa*s]Flexural strength [MPa] dry 89 94 98 104 70 80 95 96 Flexural modulus[MPa] dry 2042 2312 2655 2994 1532 1957 2500 2644 Outer-fibre strain atbreak 9.6 8.1 7.0 7.2 n.b. n.b. 11.7 9.2 [%] dry Flexural strength [MPa]wet 70 67 72 76 59 59 75 79 Flexural modulus [MPa] wet 1621 1535 18862037 1285 1462 2043 2156 Outer-fibre strain at break 9.8 7.2 7.8 7.5n.b. n.b. 10.0 9.1 [%] wet Kmax [MPa m^(1/2)] dry 1.2 1.0 1.3 1.3 1.2 —— 1.2 FW [J/m²] dry 156 97 161 150 173 — — 128 Kmax [MPa m^(1/2)] wet1.1 1.1 1.1 1.3 1.4 1.3 1.2 1.2 FW [J/m²] wet 189 170 157 206 383 282182 163 ¹⁾Triethylene glycol dimethacrylate (CAS No. 109-16-0)²⁾Urethane dimethacrylate (CAS No. 72869-86-4) ³⁾Addition product ofmethacrylic acid and bisphenol A diglycidyl ether ⁴⁾CAS No. 1360927-06-5⁵⁾CAS No. 34759-34-7 ⁶⁾Oligomer (a1) with R⁹ and R¹⁰ = H and a molarmass of approx. 2200 g/mol⁷⁾Diphenyl(2,4,6-trimethylbenzoyl)phenylphosphine oxide (CAS No.75980-60-8) ⁸⁾Mixture of a silanized glass filler with a particle sizeof approximately 0.7 μm (before the silanization) and a silanized glassfiller with a particle size of approximately 1.0 μm (before thesilanization) in a ratio by weight of approximately 2:1 ⁹⁾Prepolymerfiller (so-called isofiller, i.e. a ground composite material) with aparticle-size distribution of from approximately 0.1 to approximately 10μm n.b.: Test piece not broken

The compositions of Examples 1 to 14 were used for the additivemanufacture of three-dimensional components in a stereolithographicprocess. For this purpose, test pieces were produced by means of astereolithography printer in the bottom-up process. The printer exposedthe samples to light using the DLP technique with a wavelength of 388nm, a power of 10 mW/cm² and a pixel size of 50 μm in a layeredconstruction. The layer thickness was 50 μm in each case.

The test pieces produced in this way had a dimension of 50 mm in length,4 mm in thickness and 8 mm in height, wherein the test pieces, includinga notch with a depth of 3 mm, in the middle in each case, were printedout on the upper side of the test piece. The notch was 1 mm wide in eachcase and extended over the entire thickness of the test piece (4 mm).

After being printed out, the test pieces were cleaned and post-treated.Then, by means of a razor blade, a perpendicular cut with a depth ofapprox. 300 μm was made precisely in the middle of the notch in eachcase and the test pieces were stored in mains water (“wet”) or in air(“dry”) for 24 h at 37° C.

The determination of the outer fibre strain, the flexural strength andthe flexural modulus was effected using the above-described processaccording to ISO 4049.

The determination of the fracture toughness Kmax and the fracture workFW was effected in accordance with ISO 20795-1:2013 in the 3-pointflexural test with a support span of 32 mm. The determination of K_(max)and FW is based on the theoretical principles of the stress intensityfactor K_(1c). The fracture toughness Kmax is the highest factor of theload intensity, or also called the stress intensity factor at highestload, and is calculated as follows:

${K_{\max} = {\left( \frac{P_{\max} \cdot S}{B \cdot W^{\frac{1}{2}}} \right) - {{f(x)} \cdot 0.031}}}{{{MPa} \cdot m^{1/2}},{with}}{{{f(x)} = {{3 \cdot \sqrt{x}}\frac{1.99 - {{x\left( {1 - x} \right)} \cdot \left( {2.15 - {3.93x} + {2.7x^{2}}} \right)}}{2{\left( {1 + {2x}} \right) \cdot \left( {1 - x} \right)^{\frac{1}{2}}}}}},{{{wherein}x} = \frac{a}{W}}}$

and W is the sample piece height (=8 mm), B is the sample piecethickness (=4 mm), a is the tear length (=3 mm+tear depth with razorblade, S is the support span (=32 mm) and Pmax is the maximum pressurein the test.

The calculation of the fracture work (total fracture work) was effectedas follows:

${FW} = {{\frac{U}{2{B\left( {W - a} \right)}} \cdot 1000}J/m^{2}}$

wherein U is the total energy which is required to break the sample(integral of the load/displacement graph) and which is needed to createthe two new fracture planes B(W−a). This parameter describes theresistance of the material to the crack propagation and is dependent onthe sample dimensions and the test conditions.

1. A polymerizable composition comprising (a) at least one radicallypolymerizable oligomer, (b) at least one radically polymerizable monomerand (c) at least one initiator for the radical polymerization, whereinthe radically polymerizable oligomer (a) is an aliphatic urethane(meth)acrylate oligomer of structural formula (I)

in which R¹ and R⁵ each are —C(═O)—NH— or —C(═O)—NH—CH₂—, R³ and R⁷ eachare —NH—C(═O)— or CH₂—NH—C(═O)—, R², R⁴, R⁶ and R⁸ each are H or CH₃, R⁹and R¹⁰ each are H or CH₃, wherein, if R¹ is —C(═O)—NH—, then R² is H,R³ is —CH₂—NH—C(═O)— and R⁴ is CH₃ and, if R¹ is —C(═O)—NH—CH₂—, then R²is CH₃, R³ is —NH—C(═O)— and R⁴ is H, and M is a mid-chain segment whichis obtainable by polymerization of ε-caprolactone and2-(2-hydroxy-ethoxy)ethanol or by polymerization of1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane,ε-caprolactone and 2-(2-hydroxyethoxy)ethanol.
 2. The polymerizablecomposition according to claim 1, wherein the oligomer (a) is anoligomer of structural formula (II)

in which R¹ to R¹⁰ have the meaning according to claim 1, M′ is amid-chain segment which is obtainable by polymerization ofε-caprolactone and 2-(2-hydroxyethoxy)ethanol, and n is a whole numberfrom 1 to
 10. 3. The polymerizable composition according to claim 2,wherein the mid-chain segment of Formula (II) is described by structuralformula (III)

in which x is a number from 1 to 20, and y is a number from 1 to
 20. 4.The polymerizable composition according to claim 1, wherein the oligomer(a) has a number-average molecular weight of more than 500 g/mol or inthe range of 500 to 8000 g/mol.
 5. The polymerizable compositionaccording to claim 1, wherein the polyfunctional monomer (b) is selectedfrom the group consisting of di- and trifunctional acrylates andmethacrylates with a molecular weight of <1000 g/mol and mixturesthereof, or from the group consisting of glycerol1,3-dimethacrylate-2-acetate, 2-phenoxyethyl (meth)acrylate, aliphaticurethane diacrylates, phthalic acid 2-hydroxyethylacrylate ester,pyromellitic acid di-2-hydroxyethylacrylate ester, bis-G(M)A,2,2-bis[4-(2-(meth)acryloxypropoxy)phenyl]propane, urethanedi(meth)-acrylate, triethylene glycol di(meth)acrylate, tricyclo-decanedimethanol dimethacrylate, and the reaction product of1,3-phenylenebis(propane-2,2-diylcarbamoyloxyethane-2,1-diyl)bis(2-methylacrylate),2-{[(2-{-[2-methacryloyloxy)ethoxy]carbonyl}amino)propan-2-yl]phenyl}propan-2-yl)carbamoyl]oxy}propylmethacrylate and 1,3-phenylenebis(propane-2,2-moyloxypropane-2,1-diyl)bis(2-methylacrylate) as well as mixtures thereof.
 6. The polymerizablecomposition according to claim 1, wherein the polyfunctional monomer (b)comprises a mixture of urethane di(meth)acrylate, triethylene glycoldi(meth)acrylate and bis-GMA (an addition product of methacrylic acidand bisphenol A diglycidyl ether).
 7. The polymerizable compositionaccording to claim 1, wherein the photoinitiator (c) is selected fromthe group consisting of camphorquinone, ethyl4-(dimethylamino)-benzoate, phenylbis(2,4,6-trimethylbenzoyl)phosphineoxide, diphenyl(2,4,6-trimethylbenzoyl)phenylphosphine oxide,2-benzyl-2-(dimethylamino)-4′-morpholinobutyro-phenone,1-butanone-2-(dimethylamino)-2-(4-methylphenyl)-methyl-1-4-(4-morpholinyl)phenyl,acylgermanium compoundsand combinations thereof, or from the groupconsisting of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide,diphenyl(2,4,6-trimethylbenzoyl)phenylphosphine oxide,bis(4-methoxybenzoyl)diethylgermanium,tetrakis(4-ethoxybenzoyl)germanium, tetrakis(4-propoxybenzoyl)-germaniumand combinations thereof.
 8. The polymerizable composition according toclaim 1, further comprising a monofunctional monomer or a monofunctionalmonomer selected from the group consisting of dicyclopentanylmethacrylate, p-cumylphenoxyethylene glycol methacrylate and mixturesthereof.
 9. The polymerizable composition according to claim 1, furthercomprising a UV absorber, wherein the UV absorber is selected from thegroup consisting of2,2′-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol],2,2′,4,4′-tetrahydroxybenzophenone,2-tert-butyl-6-(5-chloro-2H-benzotriazol-2-yl)-4-methylphenol(bumetrizole), 2,2′-benzene-1,4-diylbis(4h-3,1-benzoxazin-4-one),2-(4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-(octyloxy)-phenol,2-(2-hydroxy-5-methylphenyl)benzotriazole,2-(2-hydroxyphenyl)benzotriazole,2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol,2-(2′-hydroxy-3′-5′-di-t-butylphenyl)-5-chlorobenzotriazole,2,2′-dihydroxy-4-methoxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone and mixtures thereof, orwherein the UV absorber is bumetrizole or2,2′,4,4′-tetrahydroxybenzophenone.
 10. The polymerizable compositionaccording to claim 1, further comprising up to 15 vol.-% of a filler.11. The polymerizable composition according to claim 1, comprising, ineach case relative to the total weight of the composition, (a) 25 to 60wt.-% oligomer, (b) 30 to 65 wt.-% polyfunctional monomer, (c) 0.1 to3.0 wt.-% photoinitiator, (d) 0 to 15 wt.-% monofunctional monomer, (e)0 to 2.0 wt.-% UV absorber, (f) 0 to 40 wt.-% filler and (g) 0 to 3.0wt.-% thixotropic additive.
 12. The polymerizable composition accordingto claim 1, comprising, in each case relative to the total weight of thecomposition, (a) 40 to 60 wt.-% oligomer, (b) 40 to 60 wt.-%polyfunctional monomer comprising a mixture of UDMA, TEGDMA and bis-GMA,(c) 0.5 to 2 wt.-% photoinitiator, (d) 0 to 10 wt.-% monofunctionalmonomer, (e) 0 to 2.0 wt.-% UV absorber, (f) 0 to 40 wt.-% filler and(g) 0 to 3.0 wt.-% thixotropic additive, wherein the polyfunctionalmonomer (b) comprises, in each case relative to the total weight of thecomposition, (b1) 10 to 20 wt.-% UDMA, (b2) 20 to 35 wt.-% TEGDMA and(b3) 3 to 20 wt.-% bis-GMA.
 13. The polymerizable composition accordingto claim 1, comprising, in each case relative to the total weight of thecomposition, (a) 37 to 55 wt.-% oligomer, (b) 39 to 56 wt.-%polyfunctional monomer comprising a mixture of UDMA, TEGDMA and bis-GMA,(c) 0.5 to 2 wt.-% photoinitiator, (d) 0 to 15 wt.-% monofunctionalmonomer comprising dicyclopentanyl methacrylate and/orp-cumylphenoxyethylene glycol methacrylate, (e) 0 to 2.0 wt.-% UVabsorber, (f) 0 to 40 wt.-% filler and (g) 0 to 3.0 wt.-% thixotropicadditive, wherein the polyfunctional monomer (b) comprises, in each caserelative to the total weight of the composition, (b1) 10 to 20 wt.-%UDMA, (b2) 20 to 35 wt.-% TEGDMA and (b3) 3 to 20 wt.-% bis-GMA.
 14. Thepolymerizable composition according to claim 1, comprising in each caserelative to the total weight of the composition, (a) 37 to 55 wt.-%oligomer, (b) 35 to 50 wt.-% polyfunctional monomer comprising a amixture of UDMA, TEGDMA and bis-GMA, (c) 0.5 to 2 wt.-% photoinitiator,(d) 0 to 15 wt.-% monofunctional monomer comprising dicyclopentanylmethacrylate and/or p-cumyl-phenoxyethylene glycol methacrylate, (e) 0to 2.0 wt.-% UV absorber, (f) 0 to 40 wt.-% filler, and (g) 0 to 3.0wt.-% thixotropic additive comprising SiO₂, wherein the polyfunctionalmonomer (b) comprises, in each case relative to the total weight of thecomposition, (b1) 10 to 15 wt.-% UDMA, (b2) 21 to 26 wt.-% TEGDMA and(b3) 3 to 8 wt.-% bis-GMA.
 15. A process for the production or repair ofa dental part, comprising curing a polymerizable composition as definedin claim 1 with the aid of light in order to yield the dental part. 16.The process according to claim 15, wherein the dental part is a dentalrestoration, a prosthesis, a prosthesis material, an artificial tooth,an inlay, an onlay, a crown, a bridge, a drilling template, a try-in oran orthodontic appliance selected from the group consisting of aligners,positioners, aligner attachments, positioners bearing alignerattachments, occlusal splints, transfer splints and orthodontic splints.17. The process according to claim 16, wherein the production or repairof dental parts is effected by an additive process comprising using 3Dprinting or a lithography-based process.